Terry Spragg wrote:

I can use a bicycle pump or similar to evacuate my holding tank
offshore. I close both air vents, open the sea valve, and pump up
the holding tank with air.

This is a really bad idea. The question is not *if* the tank will blow up, but
when.

The highest standard for marine tanks (including fuel BTW) and associated
fittings is .5 psi overpressure. Most are not built to withstand even that
much.

If you really have been doing this Terry, you've been very lucky (and so have
your neighbors).

Fresh Breezes- Doug King